This invention relates to abrasive articles and methods of making and using abrasive articles. More specifically, this invention relates to abrasive articles incorporating a grinding aid and methods of making and using such abrasive articles.
Abrasive articles are used to abrade and finish a variety of workpieces ranging from high pressure metal grinding to the fine polishing of silicon wafers. In general, abrasive articles comprise a plurality of abrasive particles bonded to each other (e.g. a bonded abrasive or grinding wheel) or bonded to a backing (e.g., a coated abrasive sheet). Coated abrasives commonly include the sequential layers of backing, make coat, abrasive particles and size coat. The coated abrasive can further include an optional supersize coat over the size coat. Typically, the coated abrasives include a single layer of abrasive particles and a grinding aid incorporated into one of the layers (e.g., KBF4 incorporated into the supersize coat) for purposes of increasing abrasion efficiency. Once the layer of abrasive particles are worn, the coated abrasive is spent and must be replaced. The industry is continuously seeking ways to extend the useful life of an abrasive article and/or increase the cutting rate of the abrasive article.
One attempt to extend the useful life of coated abrasives is described in U.S. Pat. Nos. 4,652,275; 4,799,939 and 5,039,311. The coated abrasives disclosed in these patents comprise a plurality of abrasive agglomerates bonded onto the upper surface of a backing, wherein the abrasive agglomerates are shaped masses of abrasive grains held together by a binder and optionally including a grinding aid and/or other additives.
Another attempt to extend the useful life of coated abrasives is described in U.S. Pat. Nos. 4,644,703, 4,773,920, 5,015,266 and 5,378,251, wherein an abrasive slurry comprising abrasive particles and a binder are bonded to a backing so as to form a lapping film.
These lapping films enjoy wide commercial success in polishing applications where a fine surface finish is desired. However, due to the limited rate of cut attainable with such lapping films, such films have enjoyed only limited success in many other applications.
Culler et al (U.S. Pat. No. 5,378,251) discloses an abrasive article comprising an abrasive slurry bonded to the front surface of a backing wherein the abrasive coating is a homogeneous mixture of abrasive particles, grinding aid and binder. Culler et al. discloses that the abrasive coating may be shaped to provide separate abrasive composites extending from the front surface of the abrasive article.
Tselesin (U.S. Pat. No. 5,190,568) discloses an abrasive article having a contoured front surface produced by coating a contoured backing with an abrasive slurry. Tselesin requires the backing to be constructed from a material which will wear quickly and be promptly removed from contact with a workpiece in order to avoid potentially deleterious contact between the backing and the workpiece.
Several different techniques have been developed for incorporating a grinding aid into a coated abrasive. It is a common practice to incorporate a grinding aid into the size coat and/or the super size coat used in the manufacture of coated abrasives.
Broberg et al. (U.S. Pat. No. 5,078,753) discloses an abrasive article containing erodible agglomerates of a resinous binder and an inorganic filler, such as cryolite, interspersed with abrasive particles. One of the embodiments disclosed by Broberg et al. includes erodible agglomerates positioned between elongated abrasive particles, wherein the erodible agglomerates and the abrasive particles are of substantially the same size.
Cosmano et al. (U.S. Pat. No. 5,454,750) discloses an abrasive article containing erodible agglomerates of a grinding aid or a combination of grinding aid and binder interspersed with the abrasive particles.
Gagliardi et al. (U.S. Pat. No. 5,578,098) discloses an abrasive article containing erodible agglomerates of a grinding aid or a combination of grinding aid and binder interspersed with the abrasive particles. One of the embodiments disclosed by Gagliardi et al. includes rod shaped agglomerates positioned between abrasive particles wherein the erodible agglomerates and the abrasive particles are of substantially the same size (i.e., ratio of maximum dimension of erodible agglomerates to maximum dimension of abrasive particles is between about 2.5:1 to about 0.5:1).
While such techniques are generally effective for incorporating effective amounts of a grinding aid into a coated abrasive, the search continues for improved techniques of incorporating a grinding aid into a coated abrasive.
We have discovered an abrasive article having an extended useful life span effective for providing abrasion enhancing amounts of a grinding aid to the surface of the workpiece being abraded. The abrasive article further provides an isolation layer between the grinding aid and the abrasive coating (i.e., make coat, abrasive particles, size coat and supersize coat), thereby permitting the use of incompatible materials in the grinding aid and abrasive coating layers.
The abrasive article includes (i) an embossed isolation layer defining inversely contoured first and second surfaces with a plurality of peaks on the first surface producing a plurality of pockets on the second surface, (ii) grinding aid-containing protrusions positioned within the pockets, and (iii) a coating of abrasive particles adhered to the contoured first surface of the isolation layer. The protrusions will generally adhere to the second surface of the isolation layer such that a backing may be provided over the second surface of the isolation layer, but is not required.
The coating of abrasive particles at the peaks formed in the isolation layer have a limited thickness such that initial use of the abrasive article wears away the coating of abrasive particles at the peaks, along with the isolation layer forming the peak, and thereby exposes the grinding aid-containing protrusions to a workpiece.
In an alternative description of the invention, the abrasive article includes (i) an embossed isolation layer defining inversely contoured first and second surfaces with the first surface having (A) a plurality of peaks defining protrusion apexes and producing a plurality of pockets on the second surface, and (B) a plurality of valleys between the peaks defining base layer nadirs, (ii) grinding aid-containing protrusions positioned within the pockets, and (iii) a coating of abrasive particles adhered to the contoured first surface of the isolation layer and defining (A) abrasive coated peaks having an abrasive coated apex, and (B) abrasive coated valleys having an abrasive coated nadir, wherein the protrusion apex of a majority of the protrusions extend above at least one adjoining abrasive coated nadir.
The invention further includes a method of making the abrasive article involving the steps of (1) embossing the isolation layer to form the pockets, (2) filling the pockets with a grinding aid-containing composition to form the protrusions, and (3) coating the abrasive particles onto the contoured first surface of the isolation layer.
The invention also includes a process for abrading a workpiece with the abrasive article involving the steps of obtaining a workpiece in need of abrasion, and abrading the workpiece with the abrasive article.